<!DOCTYPE html>
<title>Tests that anchored element's actual rendered location is property exposed via JS APIs under scrolling</title>
<link rel="help" href="https://drafts.csswg.org/css-anchor-position-1/#scroll">
<link rel="author" href="mailto:xiaochengh@chromium.org">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
#container {
  position: absolute;
  top: 0px;
  left: 0px;
}
#scroller {
  margin-left: 100px;
  margin-top: 100px;
  width: 400px;
  height: 400px;
  overflow: scroll;
}
#anchor-container {
  width: 2000px;
  height: 1000px;
}
#anchor {
  margin: 400px;
  margin-left: 1400px;
  width: 100px;
  height: 100px;
  background-color: yellow;
  anchor-name: --anchor;
}
#anchored {
  position: absolute;
  left: anchor(left);
  bottom: anchor(top);
  width: 100px;
  height: 100px;
  position-anchor: --anchor;
  background-color: green;
}
</style>

<div id="container">
  <div id="scroller">
    <div id="anchor"></div>
  </div>
  <div id="anchored">Text</div>
</div>

<script>
promise_setup(async () => {
  // Move both the anchor and the anchored elements into the visible area of the
  // scroller. This also runs layout to setup an empty scroll snapshot.
  scroller.scrollTop = 300;
  scroller.scrollLeft = 1300;

  // Ensure up-to-date scroll snapshot.
  await new Promise(resolve => requestAnimationFrame(resolve));
});

promise_test(async () => {
  let rect = anchored.getBoundingClientRect();
  assert_equals(rect.x, 200);
  assert_equals(rect.y, 100);
}, 'Element.getBoundingClientRect() returns the actual rendered location');

promise_test(async () => {
  let range = document.createRange();
  let text = anchored.firstChild;
  range.setStart(text, 0);
  range.setEnd(text, text.length);
  let rect = range.getBoundingClientRect();
  assert_equals(rect.x, 200);
  assert_equals(rect.y, 100);
}, 'Range.getBoundingClientRect() returns the actual rendered location');

promise_test(async () => {
  assert_equals(anchored.offsetLeft, 200);
  assert_equals(anchored.offsetTop, 100);
}, 'Element.offset* return adjusted offsets');

promise_test(() => new Promise(resolve => {
  let observer = new IntersectionObserver(entryList => {
    if (entryList.some(entry => entry.isIntersecting))
      resolve();
  });
  observer.observe(anchored);
}), 'IntersectionObserver should fire when anchored element is moved into visible area');
</script>
